Fog reduction in photographic silver halide emulsions

ABSTRACT

PHOTOGRAPHIC ELEMENTS HAVING THEREON A SILVER HALIDE EMULSION LAYER, AND CONTAINING IN SAID LAYER OR AN ADJACENT LAYER, A 2,2&#39;&#39;-(P,P-BIPHENYLENE)-3,3&#39;&#39;,5,5&#39;&#39;-TETRASUBSTITUTED BISTETRAZOLIUM SALT AS A FOG REDUCING AGENT.

United States Patent Int. Cl. G03c 1/34 U.S. Cl. 96109 Claims ABSTRACTOF THE DISCLOSURE Photographic elements having thereon a silver halideemulsion layer, and containing in said layer or an adjacent layer, a2,2-(p,p-biphenylene)-3,3,5,5-tetrasubstituted bistetrazolium salt as afog reducing agent.

This invention relates to photographic silver halide emulsions, and inparticular, to reduction therein of fog-especially while applyingmethods thereto to increase the speed and improve covering power.

More particularly, it relates to photographic elements having thereon alight-sensitive silver halide emulsion layer, and having incorporated insaid layer or in an adjacent layer, a non-difiusion bis-tetrazolium saltas hereinafter defined.

It is well known that silver halide emulsions may be sensitized withchemical sensitizers or with optical sensitizers. -In the case ofoptical sensitization, the optical range of sensitivity is increased;that is, the sensitivity to light of longer wavelengths. Chemicalsensitization is either the result of the formation of small amounts ofsilver sulfide or silver on the surface of the silver halide crystal.Examples of this class of chemical sensitizers are Na S O and Na SO Forthe purpose of increasing the sensitivity of photographic silver halideemulsions, many other compounds have been proposed; e.g.,polyoxyalkylene ethers and numerous derivatives thereof, quaternaryammonium, phosphonium, ternary sulfonium salts, also combinations ormixtures of alkylene oxide polymers and quaternary ammonium compounds,also condensation products of alkylene oxide with organic compoundscontaining an active hydrogen atom.

Certain compounds have been added to or brought in contact withphotographic silver halide emulsions for the purpose of increasing thepractical speed, improving the contrast and the covering power of thedeveloped silver. One determines covering power by dividing the opticaldensity at maximum density by the grams of silver per square decimeterin the developed image layer.

Compounds which have been proposed for this purpose are, e.g.,poly-N-vinyl lactams, the water-soluble polyglucose dextran,water-soluble fl-hydroxyalkyl ether of a polyvinyl alcohol,water-soluble hydrolyzed glucogen, water-soluble mannan polysaccharide,the watersoluble polyglucose laminarin, hydroxy-ethyl cellulose, andcarboxymethylated proteins.

- While these compounds serve their purpose well, they nevertheless,have also shortcomings. Some of these compounds cause higher fog andinferior storage stability.

It is an object of this invention to provide improved photographicsilver halide emulsions having a reduced tendency to fog and possessinggood storage stability also when they contain compounds as discussedabove which increase sensitivity, speed, contrast and/or covering power.

We have discovered that silver halide emulsions having reduced tendencyto fog can be obtained by inluding 3,597,213 Patented Aug. 3, 1971therein a bis-tetrazolium salt having the following general formula:

f N-N wherein R and R are aryl radicals such as phenyl or substitutedphenyl radicals wherein the substituents can be, for example, methyl,methoxy, hydroxy, chloro or nitro groups, or heterocyclic radicals suchas furyl, thienyl, pyridyl, quinolyl, napthothienyl, or benzothiazolyl;X represents hydrogen or a substituent such as methyl, methoxy orchloro; and A represents the anion of a salt-forming acid such ashydrochloric or acetic acid.

The preparation of compounds of the foregoing class is described in Ann,vol. 58 (1953) pages 16-23 and 29-44.

The compounds which we have described may be used in various types ofphotographic emulsions, e.g., nonsensitized emulsions, orthochromatic,panchromatic and X-ray emulsions. If used with sensitizing dyes, theymay be added to the emulsion before or after the dyes are added. Varioussilver salts may be used as a sensitive element, such as silver bromide,silver iodide, silver chloride or mixed silver halides. Our compoundsare especially suitable because of their non-diffusing properties inmulti-layer emulsions such as those intended for color photography,e.g., emulsions containing color-forming components. The dispersingagent in the photographic emulsion may be gelatin, or other colloids,such as collodion, albumen, cellulose derivatives, polyvinyl alcohol,polyvinylpyrrolidone, caseine. The emulsions to which we add ourcompounds may or may not contain chemical sensitizers, such as goldsensitizers or other noble metal sensitizers, sulfur sensitizers,reduction sensitizers, or accelerators, such as polyoxyalkylenes ortheir derivatives.

The quantity of the foregoing bis-tetrazolium compounds incorporated inthe silver halide emulsions is preferably from 0.05 to 0.5 mg. per molof silver halide.

The aforesaid compounds may be added directly to the emulsion prior tocoating or they may be added to an adjacentsueh as an undercoat, amiddle coat, an overcoat or a surface coating, which is adjacent to asilver halide emulsion layer of the light-sensitive element.

The following examples illustrate photographic emulsions andlight-sensitive materials in accordance with the invention, but are notto be regarded'as limiting the scope thereof.

EXAMPLE 1 A silver halide emulsion in gelatin containing 4% silveriodide and 96% silver bromide was prepared in a conventional manner andbrought up to its maximum light-sensitivity. It was then readied forcoating on film base; that is, melted at 40 C., necessary coating finalswere added such as sensitizing dyes, stabilizers and hardeners. A 0.001%solution of 2,2'-(m,m'-dimethoxyp,p-biphenylene)-bis-.(3,5-diphenyl-tetrazolium chloride) in methanol was prepared and aportion of this solution added to a sample of the above-describedemulsion containing about 0.6 mol of silver halide. A sample of the sameemulsion, but not containing the compound of our invention, served as acontrol. The so-prepared emulsion samples were coated on a suitablecellulose ester base or polyester base and dried. Samples of these filmcoatings were then exposed in a Type I-B sensitometer and developed in adeveloper of the following composition:

Water: 500 cc.

Metol: 2.2. g.

Sodium sulfite, anhydrous: 72.0 g. Hydroquinone: 8.8 g.

Sodium carbonate, monohydrated: 56.0 g. Potassium bromide: 4.0 g.

Water to make 1.0 liter.

The resulting speed, maximum density and fog after 6 minutes developmentwere as follows:

Quantity of bis-tetrazolium To a silver halide emulsion sample similarto that used in Example 1 and containing 0.6 mol of silver halide, therewas added, 1 gram of polyoxyethylene lauryl ether and ml. of an 0.001%solution in methanol of the bistetrazolium salt of Example 1. Aftercoating on a film base as described in Example 1, an aqueous gelatinsolution containing 20 g. of gelatin per liter was overcoated to providean antiabrasion layer. As a control, light-sensitive material wassimilarly prepared, omitting, however, the bis-tetrazolium compound.Samples of the resulting film were exposed and developed in the samemanner as in Example 1, yielding the following results in terms ofrelative speed, maximum density and fog after 12 minutes development:

Fog 12 Relative devel- Material speed 1),, opment- Control 150 3. 04 34Material containing bis-tetrazolium salt... 150 3. 04 23 EXAMPLE 3 Asilver halide emulsion in gelatin containing 2% silver iodide and 98%silver bromide was prepared in a conventional manner and brought up toits maximum light sensitivity. It was then readied for coating asdescribed in Example 1. Also samples were prepared as in Example 1. Testand control were then developed in a commercial rapid processing system(Eastman Kodak M4 X-Omat system). The results were as follows:

Quantity of bis-tetrazolium compound Relative used, mg. speed Fog D mu!EXAMPLE 4 The testing material (a), (b) and (c) was SI1Sis tometricallyexposed and developed in the M4 X-O'mat system, with the followingresults:

Experiment Speed Fog Dmax. Ag, gJdm.

R1 R2 X A Anisyl Phenyl Methoxyn Acetate. o-Hydroxyphenyl... d dChloride. 3,4-dimethoxyphenyl. ..do Acetate. Furyl (2) D0. Thienyl (2).Do. Pyridyl (2) Do. Thionaphthenyl (2) Do. Dibenzothiazolyl (2). ..d0Chloride Phenyl Acetate o-Nitrophenyl. Do. o-Chloropheny Do. Phenyl Do.o-Nitrophenyl Do. o-Chlorophenyl Do. Furyl ..do Chloride. Pyridyl (2).-..do Acetate Pyridyl (4) --d0 D0. Thionaphthenyl (2)- do......... ...doD0. Furyl Qulnolyl (2) .do D0. Thienyl Phenyl H Chloride.

The aforesaid salts are similarly effective when incorporated in a layeradjacent to the silver halide emulsion layer in photographiclight-sensitive material.

Variations and modifications which will be obvious to those skilled inthe art can be made in the foregoing examples without departing from thescope or spirit of the invention.

We claim:

1. A light-sensitive silver halide emulsion containing a fog-reducingamount of an antifoggant comprising a compound of the following generalformula:

wherein R and R are independently selected from the group consisting ofaryl and heterocyclic radicals, X represents a member selected from thegroup consisting of hydrogen, chlorine, methyl and methoxy groups, and Arepresents the anion of a salt-forming acid.

2. A light-sensitive silver halide emulsion as defined in claim 1,wherein said antifoggant is present in a concentration of 0.05 to 0.5mg. per mol of silver halide.

3. A light-sensitive silver halide emulsion as defined in claim 1,wherein said emulsion contains at least one member selected from thegroup consisting of sensitizers and accelerators.

4. A light-sensitive silver halide emulsion as defined in claim 1,wherein said antifoggant is 2,2'-(m,m'-dimethoxyp,p-biphenylene -bis- 3,S-diphenyltetrazolium chloride).

5. A light-sensitive photographic material comprising a base and alight-sensitive silver halide emulsion layer thereon, saidlight-sensitive material containing in a layer selected from the groupconsisting of said silver halide emulsion layer and a layer contiguoustherewith, a fogreducing amount of an antifoggant comprising a compoundof the following general formula:

wherein R and R are independently selected from the group consisting ofaryl and heterocyclic radicals, X represents a member selected from thegroup consisting of hydrogen, chlorine, methyl and methoxy groups, and Arepresents the anion ofa salt-forming acid.

6. A light-sensitive photographic material as defined in claim 5,wherein said antifoggant is included in said layer contiguous with saidsilver halide emulsion layer.

7. A light-sensitive photographic material as defined in claim 5,wherein said antifoggant is included in said silver halide emulsionlayer.

8. A light-sensitive photographic material as defined in claim 7,wherein said silver halide emulsion layer contains a member selectedfrom the group consisting of sensitizers and accelerators.

9. A light-sensitive photographic material as defined in claim 5,wherein the quantity of said antifoggant is from 0.05 to 0.5 mg. per molof silver halide.

10. A light-sensitive photographic material as defined in claim 5,wherein said antifoggant is 2,2'-(m,m'-dimethoxy-p,p'biphenylene) bis(3,5 diphenyltetrazolium chloride).

References Cited UNITED STATES PATENTS 2,694,716 11/1954 Allen et a196l09X 3,043,697 7/1962 Forogard 96109 3,071,465 1/1963 Dersch et al96l09X 3,386,831 6/1968 Honig et a1. 96109 NORMAN G. TORCHIN, PrimaryExaminer R. E. FICHTER, Assistant Examiner

